[dstructor]

I dabbled a little with DIY cont. light rig to achieve that result but no success (lots of learned lessons tho)

Question remains: What are the properties of continuous light needed to achieve infinite white (when directed at a white BG) using 1/100 f8 & ISO100

My rig (a little inefficient; a box, basically) had a total of ~3kW CFL lights but reached infinite white at ISO 400 f8 1/25 (4 f-stops less than target)
But I understand that watts is not very accurate at all in judging the actual "light" (thus the light needed) so what property of light to measure & look for?

Let me know what you think

(P.S: KinoFlo's & HMI's are pretty damn expensive, in case you were wondering if i considered them or not)

[JimJohnson]

Without looking up any of the typical terms used in photography, I'd say you are talking about volume, contrast, color temperature and color cast.

As for measuring these for items.... volume and contrast are easiest. Your camera's exposure meter works on light reflected off your subject. You would need to use spot metering and see how many stops difference there is between your most lighted and least lighted spots. For consistency, you need a uniform surface like a gray card. If the range between the two is greater than your camera's sensor can handle, you will either have blown highlights or black shadows.

I personally prefer using a separate reflected/incident light meter for continuous lighting. The reflected setting works essentially just like your camera's meter. I feel it is the incident metering mode that is more accurate. You place the meter at the subject and point it back at the camera lens. The meter directly reads the light falling on the subject. For the overall exposure, you don't even need the presence of the subject. However, to measure contrast (and therefore exposure range) you have to have the subject in place and put the incident meter in the bright spots and dark spots and measure the difference. The biggest trick is to make sure that you and the meter aren't affecting the reading.

Color temperature and color cast are tougher to measure. Together, we call this white balance. Your camera has a built-in meter, but it doesn't do a good job of giving you information before you take the shot. Stand-alone color meters exist, but frankly, the cost is prohibitive for my budget.

There are two pieces of good news and two pieces of bad news.

good- It is often easy to look up the general qualities of constant lighting sources, including color temperature and color cast.
good - if you shot RAW, you can almost ignore white balance because it is fairly easy to adjust in post-processing. You can also adjust jpegs in post processing; it just isn't as clean or easy as in RAW, so it is better to get it right before you expose.
bad- some forms of constant lighting don't output the entire frequency range of visible light. And no matter what you do, you can't filter for colors that simply don't exist in the image. Some (but not all) LED lights are notorious for having narrowed frequency ranges.
bad - you don't EVER want to mix different light sources in the same image. Unless you go crazy creating masks, tweaking individual levels, and merging the mess back into one image, you can only correct for one color temperature/color cast in each image.


Re-reading your post dstructor, I'll also point out the inverse square law about light volume. If you double the distance between the light source and subject, you will get 1/4 the light volume. Conversely if you half the distance, you will get 4 times as much volume. (-/+ 2 stops) And if you double the same type of light at the same distance you will double your light volume, and of course the inverse halves the light volume (+/- 1 stop).

[dstructor]

Without looking up any of the typical terms used in photography, I'd say you are talking about volume, contrast, color temperature and color cast.

As for measuring these for items.... volume and contrast are easiest. Your camera's exposure meter works on light reflected off your subject. You would need to use spot metering and see how many stops difference there is between your most lighted and least lighted spots. For consistency, you need a uniform surface like a gray card. If the range between the two is greater than your camera's sensor can handle, you will either have blown highlights or black shadows.

I personally prefer using a separate reflected/incident light meter for continuous lighting. The reflected setting works essentially just like your camera's meter. I feel it is the incident metering mode that is more accurate. You place the meter at the subject and point it back at the camera lens. The meter directly reads the light falling on the subject. For the overall exposure, you don't even need the presence of the subject. However, to measure contrast (and therefore exposure range) you have to have the subject in place and put the incident meter in the bright spots and dark spots and measure the difference. The biggest trick is to make sure that you and the meter aren't affecting the reading.

Color temperature and color cast are tougher to measure. Together, we call this white balance. Your camera has a built-in meter, but it doesn't do a good job of giving you information before you take the shot. Stand-alone color meters exist, but frankly, the cost is prohibitive for my budget.

There are two pieces of good news and two pieces of bad news.

good- It is often easy to look up the general qualities of constant lighting sources, including color temperature and color cast.
good - if you shot RAW, you can almost ignore white balance because it is fairly easy to adjust in post-processing. You can also adjust jpegs in post processing; it just isn't as clean or easy as in RAW, so it is better to get it right before you expose.
bad- some forms of constant lighting don't output the entire frequency range of visible light. And no matter what you do, you can't filter for colors that simply don't exist in the image. Some (but not all) LED lights are notorious for having narrowed frequency ranges.
bad - you don't EVER want to mix different light sources in the same image. Unless you go crazy creating masks, tweaking individual levels, and merging the mess back into one image, you can only correct for one color temperature/color cast in each image.


Re-reading your post dstructor, I'll also point out the inverse square law about light volume. If you double the distance between the light source and subject, you will get 1/4 the light volume. Conversely if you half the distance, you will get 4 times as much volume. (-/+ 2 stops) And if you double the same type of light at the same distance you will double your light volume, and of course the inverse halves the light volume (+/- 1 stop).

Much appreciated input, Jim
Here's more to help you tell me what i need (that you, hopefully, know )...

I understand CRI & Inv. Sq. Law.
The lights i choose are usually above 85 CRI and when lighting the background for testing they're ~50cm (1.5ft) away from the BG cloth (2 strips)
(5 months of research & trial and error teach a person a lot )

What I needed to know is in what terms should i measure light to calculate light needed?
Like I said; what i had was a total of 1.5kW CFL bulbs that gave me infinite white at 4 f-stops lower than I should

That meant that I needed 24kW of bulbs (incandescent eqv.)
BUT I was told that watts are just a measure of electricity that the bulb uses

So, what's the best terms to measure cont. light output with?
Incident light-meter at a specific distance?

Or is there anyway to convert incandescent or CFL watts numbers to lumens or lux?

[JimJohnson]

<snip> Or is there anyway to convert incandescent or CFL watts numbers to lumens or lux?

So far as I know, only in the most general of terms. You would come closest using bulbs of the same identical manufacturer/model, but even there, what is printed on the package is only within whatever manufacturing tolerances are allowed. Age also has an impact on output.

And the type of reflector also will have a big impact.

Most photographic meters read in EV (Exposure Value) units and include a scale to convert that to aperture & shutter at a specific ISO. You might come close by using an incident light meter, recording the EV changes for several controlled setups and extrapolate that against the package output to predict a future need. However, you will still only have a close approximation and will have to meter each actual scene and make adjustments.

[maxfield_photo]

In my line of work, I'm often asked the best way to do dumb things. There's really no good answer for that. People come to me with some strange way they've devised to achieve an end result, but they are so concerned with solving the problems presented by their hair-brained solutions that they never stop to wonder if there might not be a better way. I'm not saying that's the case here, but tell us a bit more about the final objective, the end product you want to achieve, there may be something simple that you're overlooking.

For high key lighting, I usually try to make my white background 1.5 stops brighter than my subject. I use Savage Super White seamless paper. If your paper is an off white, that might be a place to start. If you're using canvas, that's definitely a place to start; switch to paper. I'll have two lights to either side and I shoot them across the paper, i.e. left light points at the right side of the paper, right light points at the left side. Then I take a incident reading with my dome down on my light meter, but if you don't have a light meter, and 5 dollar gray card will do just as well. Hold or rig the gray card parallel to the backdrop and as close as you can get it, and then take a shot of just the gray card, adjust your aperture until you see a spike in the middle. That's how much light is falling on your backdrop. If my subject is f/8, I want my white backdrop to be f/13.

I will admit, I use flash, it's a little more difficult to achieve f/8 on your subject and f/13 on the background with hot lights. But why f/8 @ ISO 100? Those are hold overs from the days when ISO 100 was considered high speed, and studio photographers shot transparency film. Why not go to 800 or 1600? If the goal is the cleanest image possible, flash is much easier, if the goal is to freeze action, flash is much easier. Continuous light is great for two things, being able to see the modeling of the light, and shooting video.

[dstructor]

In my line of work, I'm often asked the best way to do dumb things. There's really no good answer for that. People come to me with some strange way they've devised to achieve an end result, but they are so concerned with solving the problems presented by their hair-brained solutions that they never stop to wonder if there might not be a better way. I'm not saying that's the case here, but tell us a bit more about the final objective, the end product you want to achieve, there may be something simple that you're overlooking.

For high key lighting, I usually try to make my white background 1.5 stops brighter than my subject. I use Savage Super White seamless paper. If your paper is an off white, that might be a place to start. If you're using canvas, that's definitely a place to start; switch to paper. I'll have two lights to either side and I shoot them across the paper, i.e. left light points at the right side of the paper, right light points at the left side. Then I take a incident reading with my dome down on my light meter, but if you don't have a light meter, and 5 dollar gray card will do just as well. Hold or rig the gray card parallel to the backdrop and as close as you can get it, and then take a shot of just the gray card, adjust your aperture until you see a spike in the middle. That's how much light is falling on your backdrop. If my subject is f/8, I want my white backdrop to be f/13.

I will admit, I use flash, it's a little more difficult to achieve f/8 on your subject and f/13 on the background with hot lights. But why f/8 @ ISO 100? Those are hold overs from the days when ISO 100 was considered high speed, and studio photographers shot transparency film. Why not go to 800 or 1600? If the goal is the cleanest image possible, flash is much easier, if the goal is to freeze action, flash is much easier. Continuous light is great for two things, being able to see the modeling of the light, and shooting video.

Well, the final result is a constant light portrait kit a pseudo-Peter Hurley/Joe Edelman set-up
The reason for the ISO 100/200 is to preserve as much detail as possible and 1/100 to avoid any movement/shake blur when shooting hand-held

I admit it; it is...dumb, for the most part but i liked the concept of constant lighting for stills & headshots and trying out something that is 1/20th the price of a KinoFlo or HMI kit didn't sound like a bad idea even if it fails (which it did)

[JimJohnson]

Well, the final result is a constant light portrait kit

I guess the lure is pretty broad...
https://www.pentaxforums.com/forums/pentax-flashes-lighting-technique/206929-...ml#post2187602
But reality soon sets in. Continuous lighting isn't necessarily less expensive or easier than flash lighting. Still, I think my constant lighting setup will be of considerable value here and there - just rarely at high shutter speeds.

[maxfield_photo]

Tell us a little about your light boxes. What's the shape, what are the lined with, what's the diffusion material (if any) that you are using. How close are they to the backdrop? Are you using the same lights to light your subject and your backdrop? Have you tried a larger aperture?

One bonus of shooting at a higher ISO is the dynamic range of the camera decreases a bit, this will actually help your whites to blow out, just expose for the shadows. But I'll tell you another secret, most high key white shots don't completely blow out, the white is usually about half a stop under that point. I think the term "infinite white" makes it sound much cooler than it really is. I would try ISO 1600 and f/4 and see where that leaves your shutter. Also if you're not already doing so, use a tripod. At 1/25th there's still a bit of danger of your subject moving while the shutter is open, but you can at least take camera shake out of the equation.

But there's also post processing that you can do. You'll probably find that the background in the center of your image is brighter than the corners. Try this, create an exposure layer in Photoshop and boost the exposure by a wide margin. Then make a mask on that layer, and do a quick and dirty selection around your subject. Then add a Gaussian blur to the mask so you don't have a hard edge. You can make this work.

[dstructor]

Tell us a little about your light boxes. What's the shape, what are the lined with, what's the diffusion material (if any) that you are using. How close are they to the backdrop? Are you using the same lights to light your subject and your backdrop? Have you tried a larger aperture?

One bonus of shooting at a higher ISO is the dynamic range of the camera decreases a bit, this will actually help your whites to blow out, just expose for the shadows. But I'll tell you another secret, most high key white shots don't completely blow out, the white is usually about half a stop under that point. I think the term "infinite white" makes it sound much cooler than it really is. I would try ISO 1600 and f/4 and see where that leaves your shutter. Also if you're not already doing so, use a tripod. At 1/25th there's still a bit of danger of your subject moving while the shutter is open, but you can at least take camera shake out of the equation.

But there's also post processing that you can do. You'll probably find that the background in the center of your image is brighter than the corners. Try this, create an exposure layer in Photoshop and boost the exposure by a wide margin. Then make a mask on that layer, and do a quick and dirty selection around your subject. Then add a Gaussian blur to the mask so you don't have a hard edge. You can make this work.

Shape: Box (10mm MDF)
Lining: Flat white paint
Diff.: Thin tracing paper
Distance from BG: 30-50cm

Gear: 2 strips (100x30x40cm) & 1 box (60x40x40cm) [LxWxD]
for each strip: 7x28w CFL (130w incand.), for box 10x28w CFL (130 incand.)

[dstructor]

now, later on i understood the extreme inefficiency of box-shape & thought about making something to be fitted with a commercial soft-box but, like i said, i needed to know the amount of light to aim for (as a 32+ CFL fixture is a bit hard & even harder to fit in a speedring so more effecient alt. like 100w bulbs...etc could be used)

But I digress; the target remains to make a cheap & powerful Portrait/Headshot constant kit that is able to take infinite white at f8 1/100 ISO 200

WHY THE CONSTANT LIGHT?!
It's not the only option as my teacher's studio & gear are available for rent to me whenever i need them
But the fact that I can talk the person i'm photographing into relaxing, loosening up & giving amazing expressions (=nice photos) seemed like something I want and very VERY hard to achieve with a strobe blasting every now & then, reminding them that they're being photographed (with all the self-consciousness that comes along)

[maxfield_photo]

Ok, here are some things to try:

• Line the inside of your strips boxes with aluminum foil, shiny side out, that should boost your output by a stop.
• Remove the diffusion material from the strips, you won't need to worry about specular highlights if the background is completely blown out.
• If you're shooting Jpeg, turn off any DR boosting features, you really only need about 3 stops for studio photography to capture your subject, and you want your background to blow out. If you're shooting RAW, turn down the recovery slider to 0, boost the exposure, drop the fill and boost the black point a bit.

Hopefully that will give you about a stop and a half more to work with. Now, let's look at the stated objective:
"... the target remains to make a cheap & powerful Portrait/Headshot constant kit that is able to take infinite white at f8 1/100 ISO 200"

The first part of the objective is solid, it's the second part where I think you're trying to do things the hard way. There are four things that you're trying to make happen, but you need to ask yourself "To what end?" Let's examine:

1) Create an "infinite" white background. This is easily achievable in post production if you really want it, but if you look closely at most high key shots they're not completely blown out, there is some gradation in the background.

2) "f/8 and be there" is the credo of the photojournalist, but they may only have one chance to snap a photo and they have to be sure that the subject is acceptably sharp and "in the can". Critical sharpness is a novel concept for them, but as a studio photographer, you have the luxury of time, and an LCD screen to tell you when you've missed. My favorite line at a shoot "That looks great, just a few more like that," translation, "I screwed up, but let's pretend like I didn't" f/5.6 should still carry acceptable sharpness from nose to ears, but sometimes I like to go even wider than that for the effect.

3) Shutter at 1/100th. This is probably the most important variable to keep if you're dealing with continuous light, but in a pinch a tripod can help you get down to 1/50th or 1/60th. Any slower than that and you may pick up subject movement, but at least you can take camera shake out of the equation.

4) ISO 200. As loathe as I am to admit it, it's not really necessary on modern DSLRs. Super low ISO is a hold over from the film days when studio photographers used to shoot slow transparency film and use a ton of light to get the finest grain possible. Back then 100 was considered "high ISO". 800 is the new 100. Shadow noise is the biggest enemy of higher ISOs, but in studio work, especially high key, the deepest shadows are rarely more then -2 stops under the working exposure.


I think if you can compromise on two of these points you should be able to make your system work. Another thought that just occurred to me is if you're trying to keep from blasting your subjects with strobes, you could still use them on the background, you'd just have to carefully gel them to match the continuous light from your CFLs.

[dstructor]

Ok, here are some things to try:

• Line the inside of your strips boxes with aluminum foil, shiny side out, that should boost your output by a stop.
• Remove the diffusion material from the strips, you won't need to worry about specular highlights if the background is completely blown out.
• If you're shooting Jpeg, turn off any DR boosting features, you really only need about 3 stops for studio photography to capture your subject, and you want your background to blow out. If you're shooting RAW, turn down the recovery slider to 0, boost the exposure, drop the fill and boost the black point a bit.

Hopefully that will give you about a stop and a half more to work with. Now, let's look at the stated objective:
"... the target remains to make a cheap & powerful Portrait/Headshot constant kit that is able to take infinite white at f8 1/100 ISO 200"

The first part of the objective is solid, it's the second part where I think you're trying to do things the hard way. There are four things that you're trying to make happen, but you need to ask yourself "To what end?" Let's examine:

1) Create an "infinite" white background. This is easily achievable in post production if you really want it, but if you look closely at most high key shots they're not completely blown out, there is some gradation in the background.

2) "f/8 and be there" is the credo of the photojournalist, but they may only have one chance to snap a photo and they have to be sure that the subject is acceptably sharp and "in the can". Critical sharpness is a novel concept for them, but as a studio photographer, you have the luxury of time, and an LCD screen to tell you when you've missed. My favorite line at a shoot "That looks great, just a few more like that," translation, "I screwed up, but let's pretend like I didn't" f/5.6 should still carry acceptable sharpness from nose to ears, but sometimes I like to go even wider than that for the effect.

3) Shutter at 1/100th. This is probably the most important variable to keep if you're dealing with continuous light, but in a pinch a tripod can help you get down to 1/50th or 1/60th. Any slower than that and you may pick up subject movement, but at least you can take camera shake out of the equation.

4) ISO 200. As loathe as I am to admit it, it's not really necessary on modern DSLRs. Super low ISO is a hold over from the film days when studio photographers used to shoot slow transparency film and use a ton of light to get the finest grain possible. Back then 100 was considered "high ISO". 800 is the new 100. Shadow noise is the biggest enemy of higher ISOs, but in studio work, especially high key, the deepest shadows are rarely more then -2 stops under the working exposure.


I think if you can compromise on two of these points you should be able to make your system work. Another thought that just occurred to me is if you're trying to keep from blasting your subjects with strobes, you could still use them on the background, you'd just have to carefully gel them to match the continuous light from your CFLs.

That was quite informative, mate

Thanks a million, I might as well try with the old rig since it's been carrying dust for a while
Also, you just reminded me that my K-01 has quite good noise reduction; will see about ISO 400 & 800

One more thing i'm curious about: when dealing with softboxes & hotlights (soft ones like CFL):
I don't use the internal diffuser so is it better to point the bulbs to the inside of the softbox or the outside? or no difference there?

[maxfield_photo]

Probably not much difference, light from those CFL bulbs is pretty omni directional. On the CFL octaboxes I've seen have the bulbs screw into the back side of the box and point at the front panel, and the the inner walls of the box are lined with silver cine foil, or something similar.